sharp-eyed

Modifies a noun

• viewer: We always welcome comments from sharp-eyed viewers who notice our errors and take the time and trouble to send us corrections.
• reader: Sharp-eyed readers will have noted the inclusion of " valid " in that list.
• observer: Only the most sharp-eyed observers will notice even the copper sulfate.
• visitor: Sharp-eyed visitors to my workshop have often asked me about an unusual instrument that inhabits this hallowed portal.
• driver: Sharp-eyed drivers are being urged to help police tighten the screw on thieves who are stealing wheels from high value cars.

Modifying Another Word

• really: If you are really sharp-eyed you may pick up the strong purposeful flight of a peregrine, or glimpse a merlin dashing by.
• very: Some very sharp-eyed lookouts spotted the floating mines before any of our flotilla made contact.